A morphometric method was developed to study changes in volumes and surface areas of gonadotropes at four hour intervals through the rat estrous cycle. These data were correlated with serum and pituitary gonadotropin levels at those times. New insights into the synthesis and secretion of FSH and LH were obtained. For instance, although the first serum peak of FSH and LH was preceded by an increase in secretory granules containing hormone, the second peak of FSH was due to the immedicate release without previous storage of newly synthesized hormone. In the research proposed in this grant, experiments are designed to manipulate the estrous cycle as a means of obtaining further insights into control mechanisms that govern the synthesis and secretion of FSH and LH. In the first aim, rats will be administered LHRH during the cycle at periods of low sensitivity, diestrus-1, high sensitivity of the gonadotropes at early proestrus and before, during, and after the late proestrus peaks of these hormones. In another experiment, pentobarbital will be administered prior to LHRH and the same experimental protocol used. In the second aim immature estrogen primed castrated rats will be given a single injection of progesterone to determine its role in FSH and LH secretory dynamics. Progesterone or estradiol will be administered to 4 day cycling rats to extend the cycle by 24 hours and to 5 day rats to shorten their cycle to 4 days in order to determine their effect on cellular organelles. In the fourth aim the effect of perphenazine induced hyperprolactinemia will be monitored throughout the estrous cycle and the effect on FSH and LH synthesis and release determined. These studies should provide new insights into control mechanisms that influence synthesis and secretion of FSH and LH and should reveal new parameters susceptible to interference in fertility control.